It appears as follows, with the text 'Absolute/Relative/Fixed/Static' highlighted:

position: Absolute/Relative/Fixed/Static;

If I overtype the selected text with the letters 'a' or 'ab' it will insert the word 'absolute'. If I Backspace to delete these characters, and type the letter 'r', it will insert the word 'relative' instead. I then tab to finish the snippet.

This is in a completions file but the same principles apply to individual snippets.

@agibsonsw: it is possible to have the trigger key in other position than begining? Let's say i want to have display: [t]able/table-[c]ell/table-[r]ow and so on. Right now i used [t], [ta], [tab] for every variant. Thanks!